This invention relates to a fastening device so constructed that an attaching base thereof is fastened to a given panel by inserting an engaging leg provided on the attaching base into a hole perforated in the panel and pushing a wedge member into an insertion hole formed within the engaging leg along the axis thereby causing the inserted wedge member to expand the engaging leg within the perforated hole of the panel and fasten it to the panel, and more particularly to the improvement in the fastening device, which improvement comprises adapting the wedge member so that after the wedge member has been pushed into the aforementioned insertion hole, it will be freely drawn out of the panel whenever necessity arises and, as a result, the attaching base which has been fastened to the panel will be freely and easily released from the panel.
Heretofore, as a measure for attaching plastic parts to electric appliances and automobiles, there have been frequently adopted methods of a common principle that required fastening of parts to their substrates is accomplished by preparatorily providing such parts with engaging legs, forming matching holes in the pertinent metal panels of the substrates and inserting the engaging legs into the perforated holes.
Methods capable of providing required fastening by the insertion of engaging legs have been proposed in a wide variety and have found utility in practical applications. Of the devices used in these methods, those which permit the parts already fastened to their substrates to be released from the attachment at will are broadly divided into two types, i.e. devices of one type which provide required attachment by simply inserting the engaging legs into the perforated holes in the substrates and devices of the other type which attain required fastening by first inserting the engaging legs into the perforated holes and thereafter driving wedge members into the engaging legs thereby expanding the engaging legs within the perforated holes.
Generally the devices of the former type are so constructed that the engaging legs having outside diameters greater than the diameters of the relevant perforated holes in the panels, during entry into the perforated holes, are allowed to contract radially by virtue of the resiliency conferred upon the legs and, after completion of engagement with the holes, the engaging legs are allowed to regain their original shapes and come into tight contact with the perforated holes. In some of these devices, the engaging legs are split into several pieces to permit ample contraction of their outside diameters. In some other of these devices, the engaging legs have hollow interiors to permit such radial contraction. Since the devices of this type are so constructed that the engaging legs thereof are attached to the perforated holes by virtue of the resilient repulsive force produced by the engaging legs themselves, the attached legs may possibly be easily removed from the holes by a pull given at strength surpassing the engaging strength. There is also a possibility that fatigue of material builds up in the engaging legs to a point where the engaging strength is weakened and the attached legs are consequently allowed to come off easily from the holes. These devices, therefore, are unfit for applications involving use of heavy parts and applications destined to expose parts to continual vibrations, though they may fit applications involving use of small parts.
In contrast, the devices of the latter type are constructed so that secure attachment of engaging legs to perforated holes is obtained by first inserting the engaging legs into the perforated holes and thereafter driving wedge members into the engaging legs thereby expanding the engaging legs within the perforated holes. The attached engaging legs will not come off the perforated holes unless the wedge members are loosed out of position. They are, therefore, suitable for applications involving use of heavy parts and applications destined to expose the parts to continual vibrations. Since the devices of the conventional principle ensuring fast engagement by use of wedge members emphasize retention of engaging legs in their securely engaged condition, they are not provided with means for aiding in release of the inserted wedge members. Generally, required release of the inserted engaging legs from the perforated holes is obtained by prying loose or totally breaking the wedge members such as with a screw driver. Particularly in the case of devices so constructed that wedge members are provided at their leading ends with radially expanded portions with a view to ensuring perfect engagement and the radially expanded portions are brought into fast engagement with the leading ends of the engaging legs which have been forced through the perforated holes and subsequently allowed to regain their original expanded form, required removal of wedge members is substantially impracticable and the release of the fastening bases from the panels is not obtained.